FIELD OF INVENTION:
This invention relates to Nano-TiO2 hybrid coating for resisting corrosion on cold
rolled steel sheet.
Further, this invention also relates to a process for producing the coating.
BACKGROUND OF THE INVENTION:
Organic titanium compounds are synthesized from TiCI4 by Nelles process. This
compounds have wide application in different fields such as reducing agents,
catalyst for esterification/trans esterification, cross linker etc. Since, these
compounds have strong affinity towards oxygen to form titanium oxide, then it
widely use in coating industries for different applications such as anti-reflective,
self cleaning, anti-bacterial and corrosion resistance coatings etc. Thin film
coating of (TiO2)x of <100 nm thin is virtually transparent and form Ti-O-Si bridge
with glass surface is a proven coated product in market. This has reduced
fragility of glass. Reflective towards heat producing IR. In hot countries, this has
been used on window glass to reduce solar heat of house. This has also been
used for solar cell application. Sometime, the mixture of ceramic materials such
as zirconates, silicates in titania used for liquid crystal devices, electronic
products etc.
Titanates are used as corrosion resistance coatings for tinplates, steels and
aluminium. The adhesion of titanates improved by chelating agents such as
acetyl acetone, 1, 2-propanediol, ethylene glycol, ethanolamine, diethanolamine,
triethanolamine, acetic acid, citrate acid, ethanol and n-butanol etc. There are
many techniques for titania deposition on substrates such as ion beam
implantation, PVD, CVD, sputtering, plasma spraying etc. All techniques have
advantages and disadvantages.

According to Jianshum Huang et al., carbon steel can be protected by titania
coatings from atmosphere. It has been shown that titania coating under solar
light acts as a non-sacrificial anode and provides cathodic protection to metals. A
good photo effect can be obtained with an interfacial layer of alpha iron oxide i.e
anatase/alpha-iron oxide/steel. This effect can further improved with a multiplayer
coating like titania(amorophous)/anatase/Ti-Fe oxide/alpha-iron oxide/steel. The
amorophous layer of titania helps in maintaining photopotential by inhibiting
oxygen reduction. Therefore, corrosion protection due to titania (anatase) coating
prolonged in day and night time. The sol required for this coating composed of
Titanium tetraisopropoxide (14.2 g), Nitic acid (0.3g), Ethanol (34.7 g) and water
(0.8 g).
OBJECTS OF THE INVENTION:
An object of this invention is to provide Nano-TiO2 hybrid coating for resisting
corrosion on cold rolled steel sheets.
Another object of this invention is to provide a process for producing Nano-TiO2
hybrid sol coating.
Further, object of this invention is to provide a Nano-TiO2 hybrid sol coating
which is corrosion resistant in saline atmosphere.
Still further object of this invention is to provide Nano-TiO2 hybrid sol coating
which can be uniformly coated on the steel surface.

BRIEF DESCRIPTION OF THE INVENTION:
According to this invention a Nano-TiO2 hybrid sol coating comprises:
Titanium precursor 69 to 100 gm
2-ethoxy ethanol 100 to 200 gm
Acetyl acetone 12.5 - 25 gm
Acetic acid 0.2 - 1 gm
Water 18-56gm
Silicon coupling agents: Glycidoxy propyl trimethoxy silane (GPTMS), [2-(3,4 -
epoxycyclohexyl) ethyl trimethoxy Silane] and [N-Phenyl - 3aminopropyl
trimethoxy Silane] 2 - 50 gm
Dyes: Tartrazine Yellow (C16H9N4Na3O9S2), Safranin - O, Methylene Blue
(C16H18N3CIS), Fluorescein-0.01-1 gm ( dyes added to get respective colours)
In accordance with this invention there is also provided a process for producing a
Nano-TiO2 hybrid coating comprising mixing titanium-precursors in compatible
solvent in a nitrogen globe box under stirring at a temperature between room
temperature to 90°C; adding water and catalyst during stirring to produce the
final sol; depositing the final sol at room temperature.
DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1a & 1b: shows that the FT-IR spectra of Ti-sol with different time of
hydrolysis without addition of acetyl acetone.
Fig 2: shows that the titania particle distribution in titania sol.
Fig 3: shows that the distribution of particle in the sol analysed by TEM.
Fig 4: shows that the TG/DTA curve of titania powder.
Fig 5: shows that the TG/DTA curves of composite powder (Titania & 10% silica)

Fig 6: shows that the XRD pattern of composite coatings (titania and silica)
sintered at 400°C.
Fig 7: shows that the XRD pattern of titania coatings sintered at 400°C.
Figs 8, 9, 10 & 11: shows that the microstructure and elemental analysis of
coatings by SEM & EDX.
Figs 12 & 13: shows that ESCA analysis of coatings.
Figs 14 & 15: shows that coating performance.
Figs 16, 17 & 18: shows that ESCA analysis at the defective region of coated
steel.
DETAILED DESCRIPTION OF THE INVENTION:
Titanates are used as corrosion resistance coatings for tinplates, steels and
aluminium. The adhesion of titanates improved by chelating agents such as
acetyl acetone, 1,2-propanedie ethylene glycol, ethanolamine, diethanolamine,
triethanolamine, acetic acid, citrate acid, advantages and disadvantages. A
bottom up technique was adopted to prepare nano-parti, of titania from its
organic compounds through chemical sol-gel process.
Sol-Gel Process: A sol-gel coating is prepared by mixing Ti-precursors in
compatible solvent in a nitrogen globe box under stirring at temperature ranges
from RT to 90°C. Hydrolysis and condensation reactions are progressed during
stirring along with addition of water and catalyst. The final sol is usually deposited
at RT and after gelation, it is dried and heated for densification.

Synthesis of Sol-Gel titania for corrosion resistance: A room temperature (RT)
sol-gel coating was sysnthesised by mixing following chemicals as given in
Table-1 & 2 under stirring in nitrogen globe box. The sol particle size and
distribution were controlled and analysed by malver particle size analyzer and
TEM respectively. It is shown in Fig. 1a & 1b Extent of hydrolysis was monitored
by FTIR. The kinetics of hydrolysis is shown in Fig. 2. Sol was deliberately
hydrolysed to form powders, this powder were under gone TGA/DTA to see the
phase changes with temperatures. This is shown in Fig. 4 & 5.
Table 1: Chemical formulation of sol-gel coatings

Chemicals Composition, gm
Titanium isopropoxide /
titanium butoxide 69-100
2-ethoxy ethanol 100-200
Acetyl acetone 12.5-25
Acetic acid 0.2-1
Water 18-56
Table 2: Chemical composition of sol-gel coating

Chemicals Composition, gm
Titanium isopropoxide /
titanium butoxide 69-112
2-ethoxy ethanol 100-224
Acetyl acetone 12.5-25
Glycidoxy propyl trimethoxy
silane (an example) 28-56
Acetic acid 0
Water 18-72
The above mixture was stirred under 300-400 rpm for about 8 hrs at 60°C.
Substrate surface preparation: Different steel grades D, EDD & IF steel sheets
were taken for the investigation. These sheets were cleaned to remove scales
and subjected to tricationic phosphate base solution to obtain a thin coating of
<0.5 micron (2-3 g/m2) phosphate coating in one case. In another case, a high

alkaline paste was prepared by mixing sodium nitrite 5 gm, sodium hydroxide 45
gm, water 40 gm, tri-sodium phosphate 10 gm and sodium vanadate 1 gm,
heated to boiling temperature under stirring for about 1 hr. Bare steel was dipped
into this paste and exposed to about 2 hrs and then washed in water and washed
steel was exposed to furnace at 525°C for obtaining alpha iron oxide. The
photographs of substrate is shown in Figs. 14 & 15. There are two, two different
substrate surface were prepared on and over that titania sol was applied.
Application of sol on steel substrate:
The synthesized sol was applied on the substrate by dipping process where
dipping time was 1 min at RT, then followed by slow drying at the rate of 5°C-
10°C for about 2 hrs then sintered at 350-500X for 30 min-1 hr at the rate of 10-
20°C. The sintered surface is shown in Figs. 6 & 7. The coating microstructure,
phases, coating elements were analysed. Corrosion performance of this coating
in saline atmosphere was investigated.
FTIR analysis: Figs. 1a & 1b shows the FT-IR spectra of Ti-sol with different time
of hydrolysis without addition of acetyl acetone. The 4000-1000 cm-1 spectra
region shows the absorption bands of the O-H stretching (3700-3200 cm-1), O-H
bending (1650-1200 cm-1) and other organic bonds vibration modes. The
absorption bands at the wavelengths from 1000-400 cm-1 are mainly due to Ti-O
vibrational modes. If the hydrolysis reaction proceed, the Ti-O-C chemical bond
will be destroyed and weakened.
After three hours of stirring, the sharp peak at 3400 cm-1 is obtained indicating
strong-OH bond has formed. This is supported by the characteristic peak of Ti-O-
C (2800 cm-1) gradually depleted. This result can be good evidence that supports
our assumption about the hydrolysis of titanium propoxide and polycondensation
of the hydrolysis products. The absorption peak from -O-C4H9 (950 cm-1)

gradually depleted. The appearance of peak at 690 cm-1 is due to presence of
Ti-O-Ti after condensation and the peak at 1650 cm-1 confirmed the presence of
hydrone in the xerogel.
Particle size analysis of sol:
Particle sizes of the optimum sol were analysed by Zitasizer. It was found that
95% particles are below 100 nm in size. This is shown in Fig: 2.
Distribution of particle in the sol analysed by TEM:
TEM was carried out to observe stable distribution of nano particles in the titania
sol. These particles are uniformly distributed throughout the sol, it indicates that it
is stable sol.
TGA/DTA analysis of powder to find phase transformation temperature:
This sol was hydrolysed and followed by condensation reaction to obtain powder
particles. The powders were analysed by TG/DTA to see its thermal behaviour.
Fig. Shows the relative mass loss (TG) and differential thermal analysis (DTA)
curves corresponding to the dried powders prepared in different methods. The
endothermic mass loss 9.6% observed for temperatures lower than 110°C can
be attributed to water and organics desorption. A significant mass loss (15.2%)
accompanied by an intense exothermic peak corresponding to the removal of
organics is apparent between 200-300°C. A release of 7.5% mass loss and
combustion (exothermic peak) of strongly bonded or adsorbed organic species is
verified between 300-400°C. The oxidation of the organic species of complexing
matter usually takesplace within this temperature range, as indicated by
complexing linkage between titania atoms and organics. The presence of
complexed form of acac was confirmed by FTIR spectra of dried powders. The
composite powder of titania and silica was shows a endothermic peak below

110°C is due to water loss. The strong exothermic peak between 210-300°C is
due to loss of organic species.
XRD analysis of coated steel:
X-ray diffraction analysis was performed at room temperature on a PANalytical,
Austrilla. The strong Mo Ka radiation (40 kV, 60 mA), a divergence slit of 10, a
scatter slit of 10, a receiving slit of 0.3 mm, 20 scan step of 0.020 and the curved-
crystal graphite monochromator for the diffracted beam were used. The XRD
analysis was done on the titania coatings (without sintering) and titania coatings
(with sintering 400°C). It was found that amorphous peak was observed without
sintering and nano crystalline anatase XRD patterns was observed at 400°C
sintering. XRD pattern of composite coatings on steel at 400°C sintering
temperature shows nano crystalline structure of titania and silica.
ESCA analysis of coatings:
The Ti 2p region obtained on the surface of a titania film produced by sol-gel
process. Two pronounced features are observed at binding energies of 459.8 ev
and 465.5 ev, evoked by the Ti 2p3/2 and Ti2pl/2 states respectively as shown in
figs 12 & 13. The measured binding energy of the Ti2p3/2 peak and the splitting
of the doublet is 6 ev indicating an oxidation state of 4+ for titanium. This also
indicates that there is no suboxides such as TiO, Ti2O3 & Ti3O5 on the surface.
This values is slightly different to the titania coating produce su are ch as by
other techniques such as IP & RE. Small differences may be due to the
difference in oxidation state or structural arrangement of the atoms.
Coating performance: SST was carried out to see its corrosion resistance
properties. It was found that nano-titania coated steel is giving 96 hrs SST
resistance as compared to 2hrs in case of bare steel.

Explanation: The portion in titania coating was found corroded. This is due to
cracks in the coatings. It was analysed by ESCA. It was found that the defective
region have very less titania coatings as depicted in figures 16, 17 & 18. It was
found prominent iron and oxygen peaks.
The samples after coating with addition of [2-(3,4 - epoxycyclohexyl) ethyl
trimethoxy Silane] and [N-Phenyl - 3aminopropyl trimethoxy Silane] formulation
enhanced life more than 168 hrs. in Salt Spray Test Bath.
To improve Corrosion resistance , hydrophobicity and elegant look, four different
dyes Tartrazine Yellow, Safranin - O, Methylene Blue, Fluorescein have been
used. Out of all the above, addition of Tartrazine yellow has enhanced life from
168 hrs. to 200 hrs.
The formability was found acceptable on coated sheets by above said coatings.

WE CLAIM:
1. A Nano-TiO2 sol coating comprises:
Titanium precursor 69 to 100 gm
2-ethoxy ethanol 100 to 200 gm
Acetyl acetone 12.5 - 25 gm
Acetic acid 0.2 - 1 gm
Water 18-56gm
Coupling agents 2-50 gm
Dyes 0.01-1 gm
2. The nano-TiO2 sol coating as claimed in claim 1, wherein the said Titania
precursor is selected from Titanium isopropoxide and titanium butoxide.
3. A process for producing a Nano-TiO2 sol coating comprising:
mixing titanium-precursors in compatible solvent in a nitrogen globe box
under stirring at a temperature between room temperature to 90°C;
adding water and catalyst during stirring to produce the final sol; coupling
agent and dyes were added after the sol formulation;
depositing the final sol at room temperature.
4. The process as claimed in claim 3, wherein the said titanium precursor is
selected from titanium isopropoxide and titatium butoxide.
5. The process as claimed in claim 3, wherein the said solvent is 2-ethoxy
ethanol is better compatible for the hydrolysis and condensation with
water addition.

6. The process as claimed in claim 3, wherein the said catalyst is acetic acid
to help stabilize the sol in presence of coupling agents like [2-(3,4 -
epoxycyclohexyl) ethyl trimethoxy Silane] and [N-Phenyl - 3aminopropyl
trimethoxy Silane].
7. The process as claimed in claim 3, wherein the step of deposition of the
sol is preferred after the gelation and then it is dried and heated for
densification.
8. The process as claimed in claim 7, wherein the said sol is applied on the
substrate by dipping process at room temperature, followed by slow drying
at the rate of 5°C to 10°C for about 10 min - 2 hrs and then sintered at
350°C-500°C for 30 min to 1 hr at the rate of 10 to 20°C.

A Nano-TiO2 sol coating comprises:
Titanium precursor 69 to 100 gm
2-ethoxy ethanol 100 to 200 gm
Acetyl acetone 12.5 - 25 gm
Acetic acid 0.2 - 1 gm
Water 18 - 56 gm
Coupling agents 2 - 50 gm
Dyes 0.01-1 gm